|Year|Conservative councillors|Labour councillors|Independent councillors|Liberal councillors|
|---|---|---|---|---|
|1947|3|2|18|1|
|1951|5|2|17|0|
|1952|3|3|18|0|
|1953|4|3|17|0|
|1954|3|4|17|0|
|1955|2|5|17|0|
|1956|2|6|16|0|
|1957|2|5|17|0|
|1958|2|6|16|0|
|1960|2|5|16|1|
|1961|2|5|15|2|
|1963|2|6|12|4|
|1964|3|6|11|4|
|1965|4|5|11|3|
|1966|9|4|6|5|
|1967|9|4|9|2|
|1972|10|10|3|1|

Question: how many years had at least 15 or more independent councillors?
Answer: 11